1. Field of the Invention
The present invention is directed to compositions useful as extrusion lubricants for vinyl halide resins, to processes for producing such compositions and to processes for lubricating vinyl halide resins during extrusion.
2. Description of The Prior Art
Vinyl halide resins, including polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polyvinylidene chloride (PVDC) and copolymers thereof, and other thermoplastic extrusion compositions have been advantageously extruded with various types of extrusion aids (microingredients) which are well known in the art. One type of well known extrusion aid, commonly known as extrusion lubricant compositions, contains paraffinic hydrocarbon waxes admixed with calcium salts of fatty acids such as calcium stearate. These additives are customarily preblended with thermoplastic extrusion compositions, such as PVC resin compositions, prior to extrusion. To facilitate blending, it is preferable that the additives be in a solid free-flowing form as flakes, granules, powders or pills. Solids in any of these forms are easier to weigh and transfer to a mixer for each batch blended. It is also desirable to combine various components into one product in order to reduce the number of weighings required for each batch of thermoplastic resin blended. The hydrocarbon and polyethylene waxes used in extrusion lubricants can be melted together and flaked, granulated, pilled or powdered. The calcium stearate compound, however, is not compatible with the waxes and cannot be simply blended with the waxes. The calcium stearate is commonly supplied as a powder. Physically blending the calcium stearate with the wax in powder form would result in undesirable separation of the calcium stearate and wax during handling due to differences in particle size and density of the two materials.
Calcium stearate can be made compatible in paraffinic waxes by heating to temperatures in excess of 150.degree. C. as disclosed in U.S. Pat. No. 3,883,362; 3,883,363; 3,979,345; 3,986,995 and 4,248,747. As disclosed in these patents, the calcium stearate may be an initial component or may be formed in situ. A uniform friable melt is obtained, whether or not the calcium stearate is formed in situ, providing a partial solution to the problem. The disadvantages of these methods include the high temperatures needed which can not be readily achieved by conventional steam heating except through high pressure lines, electrical heaters, or oil heat exchangers, which are not available to many processors and result in high energy consumption. A primary disadvantage which occurs, even when the calcium stearate is formed in situ by these prior art methods, is the high viscosity which results when the calcium stearate goes into the wax, making the processing and handling of the finished product difficult.
Another procedure for incorporating calcium stearate into paraffinic waxes involves precipitation from water, as disclosed in U.S. Pat. No. 3,909,472. This method also has disadvantages in that excessive handling is required and high energy consumption occurs. The waxes and free acid are melted in a kettle and transferred to a separate kettle containing the water/calcium base slurry. Excess energy is consumed in heating the water and in drying the precipitated product. This basic procedure is likewise utilized for the production of pure calcium stearate (no wax used) in U.S. Pat. No. 3,803,188 and lead stearates in U.S. Pat. No. 2,650,932.
U.S. Pat. Nos. 4,040,996 and 4,040,997 disclose methods for preparing aqueous dispersions. However, such dispersions have the disadvantages of longterm instability, high shipping costs if the water dispersion is shipped, and complicated production procedures and high energy consumption if the product is coated on a filler and dried.
U.S. Pat. No. 4,544,694 purports to overcome many of the disadvantages of the foregoing methods by utilizing a fatty alcohol or polyalcohol in the extrusion lubricant composition. Specifically, it is disclosed that extrusion lubricants can be prepared by combining appropriate predetermined amounts, or forming a homogeneous melt of a fatty acid and fatty alcohol or polyalcohol, adding a metal base material to form the metal salt of the fatty acid in situ, and adding one or more waxes to the mixture.
Extrusion lubricant compositions have now been discovered which obviate many, if not all, of the disadvantages and problems with prior art extrusion lubricants with the added advantage of synergizing heat stabilization of the vinyl halide resin during extrusion when an organotin or organoantimony heat stabilizer is employed.